It is known to use electronic sensors to provide an indication of the relative position between two parts of a piece of apparatus. An example is an electronic proximity sensor arranged to determine when a bogie beam of an aircraft landing gear has adopted a predetermined position relative to a slider, thereby indicating that the aircraft has taken off.
Known sensors or indicators can however be difficult to interrogate by a person trying to determine whether one part of an apparatus has assumed a predetermined position relative to another part of the apparatus, particularly where the interrogation occurs after the event as would be the case during a post-flight examination of an aircraft landing gear.